Methods have been developed which enable several biogenic amines (including both the catecholamines and the trace amines) and their metabolites to be determined in brain and urine samples. The amines were measured by gas chromatography/mass spectrometry (GC/MS) by forming the N-dinitrophenyl, O-trimethylsilyl derivatives (Edwards, Doshi and Hanin, Anal. Biochem., in press). With these methods, we have found that the concentrations of phenylethylamine increase approximately 23-fold following treatment with the MAO-inhibitor, pargyline, whereas phenylethanolamine (PEOH) shows a much smaller (two-fold) increase. GC/MS has also been used to measure the neutral deaminated metabolites of the biogenic amines, including both the phenylglycols and the phenylethanols. Phenylethylene glycol (PEG), the major deaminated metabolite of PEOH, was identified and quantitated in both human and rat urine (Edwards and Rizk, Clin. Chim. Acta, in press). Free PEG excretion was 2.7-fold higher in a group of untreated phenylketonuric patients than in a group of non-PKU controls. The same PKU patients also had a greatly reduced excretion of MHPG, the primary metabolite of norepinephrine. Several other neutral metabolites have also been conclusively identified in urine and the effects of antidepressant agents on their levels are being studied.